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Bone is an important part of your body. It provides structural support for vital organs such as heart and lungs, protects the brain and allows your limbs to move, with help of attached muscle.

Bone also can serve as a source of minerals, such as calcium and phosphorus, when needed for a variety of biological activities. Bone even can trap harmful minerals such as lead.

Bone is a living tissue that constantly is broken down (resorption) and rebuilt (formation) throughout a person's lifetime. This process is called bone remodeling. Such remodeling is an important process of normal body function. For example, remodeling can help repair damage and clear away old bone, while building new bone.

There are two types of cells in bones that work together to control this remodeling process. One is called "osteoblasts" or bone forming cells, and the other is called "osteoclasts" or bone resorbing cells. The work of these cells eventually determine bone mass.

In general, women reach their peak bone mass, or maximum bone strength and density, from age 25 to 30. Men reach their peak bone mass from age 30 to 35. After that, the remodeling balance is shifted in favor of resorption, which results in decreasing bone mass and strength. The reasons for this balance shift are complex and may involve many factors, such as changes in hormones and nutrition, physical activity, smoking and medications.

Osteoporosis

Did you know that if this imbalance remodeling is left uncorrected, osteoporosis may occur?

Osteoporosis is a disease condition in which bones become porous and fragile. It is one of many health problems affecting quality of life for aging Americans. An estimated 10 million Americans older than 50 have osteoporosis, while another 34 million are at risk. In other words, one in two women and one in eight men 50 years of age or older either have or are at risk of having osteoporosis. In addition, each year, an estimated 1.5 million people suffer an osteoporotic-related fracture.

After menopause, women are more at risk of developing osteoporosis than men. That's because during menopause, the production of a hormone called estrogen, which helps prevent bone loss, decreases.

Getting adequate dietary calcium, vitamin D, magnesium, zinc and protein is essential for healthy bones. Yet, researchers have found that physical activity is by far the most effective way to prevent or reduce the incidence of osteoporosis. The good news is that exercise is something you can do daily.

Similar to the way muscles get bigger and stronger the more they are used, bones also grow more dense and strong the more they are used. Bone is particularly responsive to the impact of weight-bearing exercise. Weight-bearing exercise is an activity that makes you work against gravity.

Bone loss

Without weight-bearing activity, bone loss occurs. Such bone loss is more pronounced in people who must undergo extensive bed rest. Consider astronauts, whom you may have seen on television, who actually float during space flight.

While it's fun to watch, you may not realize that these astronauts are experiencing tremendous bone loss. That's because of the very low gravity they experience during space flight. Scientists have found that the amount of bone loss experienced by an astronaut during one month in orbit is as much as the bone loss experienced by a typical elderly woman in a year.

What we can learn from these astronauts is that weight-baring exercise is very important to bone health and the gravity that we enjoy every day is an important part of bone metabolism.

There are many weight-bearing activities from which you can choose to help you build healthy bones. They include walking, jogging, hiking, running, volleyball, basketball, racquetball, soccer, tennis, stair climbing, jumping rope, dancing, weight lifting, swimming and more. The effects of these different exercises on bones may vary. But as long as you are physically active, you are doing your bones a favor.

In addition, regular exercise also can reduce the risk of other chronic diseases such as type 2 diabetes, hypertension, chronic heart disease and muscle wasting.

Exercise wisely

To get the most out of your health routine, exercise wisely and safely. If you haven't been exercising regularly or if you have low bone mass, you are encouraged to check with your doctor, and you should start to increase the intensity of your activity slowly and avoid "high impact" exercises. You still can exercise even if you already have osteoporosis, but you should consult with your doctor to learn how to do it safely.

Physical activity and diet are two core components of the new, interactive and individualized MyPyramid, which is sponsored by the U.S. Department of Agriculture. It is recommended that adults engage in at least 30 minutes and children in at least 60 minutes of moderate physical activity daily. Visit MyPyramid.govfor more information about the recommendation on what kind, and how much, physical activity is right for you. The message is simple: Being physically active can help you build healthy bones.